The need for applying an extremely thin layer of a coating material to a substrate or work piece arises in a number of different contexts. For example, the preparation of a thin coating is an essential step in the manufacture of micro-miniature semi-conductor electronic circuits, commonly known as "chips."
It may be necessary to make such coatings very thin indeed, as for example, a thickness of one micron or less. Furthermore in the manufacture of semi-conductor products it often happens that surface portions of the semi-conductor substrate must be cut away in order to form electrical circuits having the desired characteristics. It is then necessary to apply a thin layer of photo resist material over the semi-conductor, and it is quite important that the layer of photo resist material be of uniform thickness despite the unevenness of the surface upon which it is applied.
Another of many specific problems is known, for example, as edge build up. This is a non-uniform thickness of the coating material that occurs when a spin coating process is employed. A further problem is contamination of a liquid layer.
The object and purpose of the present invention, is to provide a high speed continuous process for applying a thin uniform coating of a liquid material, and for drying the coating, together with suitable apparatus for carrying out such process.